As an alternative device for a conventional hard disk drive (HDD), in which various data are stored, there is known a high-capacity storage device that includes a flash memory as a storage element. This storage device is generally called a solid state drive (SSD). The SSD has advantages of a shorter access time compared to the HDD, a low likelihood of a failure by a physical impact, and the like. However, the writing speed is slower than the reading speed, and therefore, it includes a problem in that the response time in a reading access increases when write commands are issued in concentration before the read command.